Related Companies and development partner Hudson Companies just topped off Riverwalk Park on Roosevelt Island, a 21-story rental apartment building on Main Street that will have 340 new affordable housing units.

Opening is set for 2021.

It’s the eighth building by Related and Hudson and the first newly built and permanently affordable one on the island.

Riverwalk Park will have a mix of studios and units of one to three bedrooms available to families with household incomes ranging from 40% to 165% of median area income.

Applications will start in 2020 through Housing Connect, the city’s housing lottery system.

Income-based rents start as low as $505 for a studio and go up to $3,431 for a three-bedroom.